JEE Main levelSingle correct optionDifficulty 2 of 3st136
Which statement about the two geometric isomers of 1,3-dimethylcyclohexane is correct?
AThe trans isomer is more stable because it can adopt a diequatorial chair
BThe two isomers are equally stable because each has one axial and one equatorial methyl group in its best chair
CThe cis isomer is more stable because it can adopt a chair with both methyl groups equatorial
DThe trans isomer is more stable because the two methyl groups are farther apart
Answer: C
In 1,3-disubstituted cyclohexanes cis = (eq,eq) or (ax,ax), while trans = (ax,eq) in both chairs. The cis isomer therefore has a chair with no axial methyl, which is about 7.3 kJ/mol more stable than either chair of the trans isomer.